.header__button-close {
  grid-area: btn;
  display: none;
  width: 40px;
  font-size: 26px;
  font-weight: 900;
  background-color: inherit;
  border: 0;
  color: rgb(255, 255, 255);
  transition: opacity .5s ease;
}

.header__button-close:hover {
  opacity: .6;
}

@media screen and (max-width: 640px) {
  .header__button-close {
    display: block;
  }
}